Broader contextAlthough public support for the expansion of nuclear power is increasing, significant growth is liable to be hindered or even halted by the seemingly intractable nuclear waste problem. A particularly difficult component of the waste problem is that any solution must be highly predictable at time scales not conducive to direct experimental verification. However, we have recently discovered a phenomenon that may permit improved predictability of long-term waste form performance. Specifically, from first principles theoretical methods, we have found that unconventional compounds and crystal structures may formviathe chemical transmutation that occurs during radioactive decay (e.g.rock salt137BaCl formation from the β- decay of137CsCl) (C. Jiang, C.R. Stanek, N. A. Marks, K. E. Sickafus and B. P. Uberuaga,Phys. Rev. B: Condens. Matter Mater. Phys., 2009,79, 132110). We refer to this phenomenon as “radioparagenesis.” For crystalline nuclear waste forms, understanding this phenomenon and its consequences may allow us to examine stability far beyond what is accessible by experiments. More importantly, we may also be able to use insight gained from radioparagenesis to revise how waste forms are designed.